Purpose: The fate of inhaled nitric oxide (NO) has not been precisely defined in critically ill patients. This study aimed at defining the effects of long-term NO inhalation on circulating NO byproduct levels.
Material and methods: During NO therapy, plasma and urine from 13 critically ill patients were sampled daily for determination of the stable byproducts of NO (nitrite [NO2-] and nitrate [NO3-]. Routine monitoring data included inhaled NO concentration, hemodynamic parameters, arterial blood gases, creatinine clearance, and C-reactive protein.
Results: For the first 24 hours of NO inhalation (6.3+/-1.1 ppm), NO3- plasma concentration increased (from 13.3+/-5.4 to 52.3+/-17.6 micromol/L), but NO2- plasma concentration was not affected. The NO3- plasma concentration was correlated with the C-reactive protein level, the inhaled NO concentration. Renal excretion of NO metabolites was unaltered by NO inhalation. The NO3 concentrations returned to baseline when NO therapy was discontinued.
Conclusion: Long-term NO inhalation was associated with a consistent increase in the NO3- plasma concentration. NO byproducts may be implicated in the systemic effects associated with this treatment.